Family members wanted to share this photo of 8-year-old Martin Cobb, who was killed while trying to save his 12-year-old sister from a rapist. (Source: Cobb family)

RICHMOND, VA (WWBT) -

Richmond Police have a warrant for the arrest of a teen in connection with a brutal South Richmond murder and rape.

Sources say the teen is being evaluated at the Tucker Pavilion at Chippenham Medical Center. Police say he killed 8-year-old Martin Cobb when he tried to stop the suspect from raping his 12-year-old sister.

Family members and friends say the girl and her brother were playing on the train tracks in the 200 block of Brandon Road, not far from their home Thursday evening. Police say the suspect sexually assaulted the girl and, when her brother tried to intervene, beat the boy to death.

Initially, the suspect was described as a white male with scraggly facial hair. Now police say the suspect, a teenage black male, threatened the victim into giving false information. No other details have been released at this time.

Family members say both children were students at Elizabeth Redd Elementary school. The boy who was killed was in first grade. His sister was in fifth grade.